Extrusion and Drawing of Metals

Definitions

Extrusion is defined as the process of shaping material, such as aluminum, by forcing it to flow through a shaped opening in a die. Extruded material emerges as an elongated piece with the same profile as the die opening.

Drawing is defined as the process of shaping material, such as aluminum, by pulling the material through a shaped opening in a die (draw die).

This process of drawing is not to be confused with the drawing process related to the forming of sheet metals

Extruded itemsRailings for sliding doorsWindow framesTubing having various cross-sectionsAluminum laddersNumerous structural and architectural shapes

Drawing ProductsRods and wires:

Including : Rods for shaftsMachine and structural componentsElectrical wiringCablesTension-loaded structural membersWelding electrodesSpringsPaper clipsSpokes for bicycle wheelsStringed musical instruments

Types of Extruding Process

Direct (forward) extrusionIndirect (reverse, inverted, or backwards) extrusionHydrostatic extrusion

Direct Extrusion Operation

Properties Extrusion process actually increases the properties of metals, because it allows the creation of a final end product that is stronger and more resilient than components that must be assembled. It allows for the fabrication of products to various specifications and sizes, while being flexible enough to allow for design alterations.

Log table

FurnaceThe extrusion process starts with the furnace, where aluminum billets are heated to the necessary point of malleability. The aluminum or aluminum alloy is heated to temperatures ranging 750 to 900 degrees Fahrenheit, at which temperatures it acts as a malleable solid.

MetalsCommon metals used in extraction process:AluminumCopperSteelsStainless steelsMagnesiumLead

Other metal alloys can be extruded with various levels of difficulty

Typical Horizontal Hydraulic Extrusion Press

Typical Horizontal Hydraulic Extrusion PressAt this point, aluminum is a soft solid that can be pressed through dies, using scaleable amounts of pressure - a process called extrusion.An extrusion press utilizes a hydraulic ram that applies between 100 to 15,000 tons or more of pressure. The extrusion press container chamber, which holds the billet, is made of steel.

Die Slide, Tooling Assembly

Photos showing a new length of extrudate, just emerging from the press (left) and the production of a profile in progress (right).ProfileThe aperture in the die represents the final product. The aluminum is pressed through the chamber and through the die to create the final, shaped profile.

DiesA solid die, as shown here, produces shapes without any enclosed voids and/or semihollow conditions

This process allows designers and engineers freedom to create products in complex and intricate shapes, since the end product can be extruded as a final piece instead of requiring multiple ones that must be assembled.

Dies ContinuedThe extrusion process also creates a natural finish - a thin layer of aluminum oxide - that forms on the surface of the metal as a result of the process. This naturally resilient and attractive finish can be improved with additional beautifying and weather-resistant finishes.

A semihollow die also produces shapes without enclosed voids; however, unlike a solid die, it produces shapes with a tongue ratio of 3:1 or greater.

Dies ContinuedComplex shapes may emerge from the extrusion press as slowly as one foot per minute. Simpler shapes can emerge as quickly as 200 feet per minute.

A hollow die produces shapes with one or more enclosed voids. The die shown here, when used together with a mandrel and other support tooling, produces a profile with six voids.

Flow through a dieExtrusion PrinciplesThe force required for extrusion depends on:The strength of the billet materialThe extrusion ratio Ao/Af Friction between the billet and the chamber and die surface

The geometric variables in extrusion are:The die angleThe ratio of the cross-sectional area of the billet to that of the extruded product, Ao/Af The temperature of the billetThe speed at which the ram travelsThe type of lubrication

BenifitsA benefit to extrusions and Drawing process would be that large deformations can take place without fracture, because the material is under high triaxial compression during the process.Since the die geometry remains constant throughout the process extruded products have a constant cross-section

Characteristics of Sheet-Metal Forming Processes

Drawing - shallow or deep parts with relatively simply shapes.Explosive Large sheets with relatively simple shapes.Magnetic Pulse Shallow forming, bulging, and embossing operations on relatively low-strength sheetsPeen Shallow contours on large sheets Roll Long parts with constant simple or relatively complex cross sections.Rubber Drawing and embossing of simple or relatively complex shapes.Spinning Small or large axis-symmetric parts, good surface finish.Stamping includes punching, blanking, embossing, bending, flanging, and coining.Stretch Large parts with shallow contours.Superplastic Complex shapes, fine detail and close dimensional tolerances.

ShearingPunch Force

F = 0.7TL(UTS)Die CuttingFine blankingSlittingSteel RulesNibbling

Miscellaneous cutting methods

Laser-beam cuttingWater-jet cuttingFriction sawingFlame cuttingCutting with band saw

Characteristics of MetalsElongationYield-Point ElongationAnisotropy (planar)Anisotropy (normal)Residual Stresses

SpringbackWrinklingQuality of sheared edgesSurface condition of sheet

Examples of sheet metal parts

BendingBeyond yield strength but below the ultimate tensile strengthPlaced on die and bent using a simple punch.

Bending Mechanism

Spring-back

Press Brake Forming Two- Stage Lock SeamChannel formingJoggleHemmingOff- Set forming

Four- Slide Machine

Rapid production 60-240 parts/minOpposite directionsSmall parts Bend > 90

Clips for eyeglass cases!

Roll Bending/ FormingUsed for bending boilers, cylindrical pressure vessels, and any other curved structureFlexible adjustments

PICTURE FRAMES

Tube Bending and FormingWork-piecePressure BarClamp

* Internal filling is sometimes necessary to prevent collapse.

Tube Bending and Forming

Stretch FormingMetal stretched across male die and clamped on edgesCommonly used to mold aircraft wing-skin panels. Low volume production

Rubber Forming?Thin strip of rubber placed on punch.Advantages

Resistance to abrasionResistance to cutting or tearingLong fatigue life

Additional OperationsBeading- sheet metal bent into cavity

Flanging- edge bending of sheet metalBulging- tubular expansion

Deep Drawing

BlankingDeep DrawingRedrawingIroningDomingNeckingSeamingRelatively complex 3 dimensional shapes can be made out of sheet metal!

Examples of Deep Drawing

Spinning and Forming

What is Spinning?Spinning is the process of forming sheet metals or tubing into contoured and hollow circular shapes.

AdvantagesLow costHigh work rate

TypesConventionalSheerTube

Conventional SpinningGreat for conical shapes

Conventional- Mandrel

Conventional- Tools

Sheer SpinningUses rollers Faster than conventional

Sheer Spinning

Sheer Spinning

TubeGreat for tubesSimilar to Sheer- reduces thickness from the inside or outside

FormingSuperplastic/Diffusion BondingExplosiveMagnetic-pulsePeenLaserMicroElectrohydraulic

SuperplasticSuperplastic is a state when material has high ductile elongation within certain temperature rangesCommon superplastic alloys: zinc-aluminum and titanium alloy

AdvantagesComplex shapesLittle or no residual stressAble to use tool with lower strength- low tooling cost

DisadvantagesMaterial must not become superplastic at service temperatureLow strain rates

Diffusion Bonding/SuperplasticUsed for parts of aircraftsHigh stiffness-to-weight ratio

Diffusion Bonding

ExplosiveUses shockwave (pressure) to force formation Material must be ductile at high rate of deformation

Explosive

Magnetic-PulseUses magnetic force discharged from a magnetic coil Material must have electrical conductivity

Magnetic-Pulse

Peen Forming

Peen FormingUsed to produce curvature by discharging steel balls (little hammers)Material shaped by shot peen has higher resistance to flexural bending fatigue

Peen Forming

Laser FormingUses laser to heat material locally for formingLaser causes thermal stress and deformationFor bending or straightening

During Pass

After Pass

Result

MicroformingA family of process that produce small metallic parts

ElectrohydraulicSimilar to Explosive formingDischarges energy between electrodes to create shockwavesUsed under water medium to develop pressureLess energy than Explosive

Electrohydraulic

Sheet Metal Forming TechniquesBlankingStampingPressingDrawingDeep Drawing

Cost Optimization With BlankingParts should be nested into patterns to reduce scrap metalPatterns should fit the sheet of metal they will be punched from to minimize waste

Producing Better BlanksIf blanks are not cut properly, the metal can be stretched be cutting instruments as it is shearedThis can lead to microcracks and distortion in the blank

Microcracks can lead to cracks and distortion as a blank is shaped

Stamping, Drawing, PressingMetal clamped around edges and forced into cavity by punchMetal can wrinkle, fracture, buckle, or not bend properly

Design to Increase Bend PrecisionNotching flanges to be bent can prevent bucklingHoles placed close to bends can lead to warping in the bends. Flanges should be notched to prevent tearing of the metal when they are bentReduce localized necks, as these can lead to tearing.

Examples of Metal Failures in Forming

Equipment for Sheet Metal FormingMost machinery used to press metal use hydraulic or pneumatic pressing, or a combination of the twoBlanks are pressed into a die specific to the design

Machine for making blanks

Factors for Press SelectionType of formingSize and Shape of DiesSize and Shape of Work piecesLength of stroke of the slides, operating speedNumber of slides: Single, Double, or Triple action press

More Factors for Press SelectionMaximum force required vs. press capacityType of pressPress control systems (computer, mechanical, etc)Features for changing diesSafety of machine operators

Example of Blanking MachineState of the art blanking machine by Minister Machine CompanyHigh speed machine for forming high strength metals, uses 1,000-ton press

This is necessary as metals such as steel continue to be made stronger

Other Examples of Metal forming machinerySteel slitting machine, used to create strips that can be quickly stamped into blanks

Metal bending machine for tight angles

Economics of Sheet-Forming OperationsSmall, simple parts are very cheap to makeThis is because large numbers of pieces can be made quickly, and the cost per part is minimizedLarge parts, such as aircraft body paneling, can be very costly to makeCost varies substantially based on thickness of sheet formed

Equipment CostsMachines used in manufacture can be expensive to purchase and maintainHowever, these are largely automated, and the cost of labor is reduced

Many sheet-formed parts need to be hand finished to remove things like burrs on the sheared edges

Burred edge

ConclusionSheet forming is good for applications where large numbers of parts can be made from sheet metal. Sheet metal pressing becomes cheaper than other manufacturing processes ~700 units Parts and manufacturing processes must be designed so parts are formed correctly and quickly

Works citedHosford, William F. Sheet Metal Forming: A Review. http://www.tms.org/pubs/journals/JOM/9911/Hosford-9911-text.html. Oct 10, 2005. 1999. Seo, Young. Blanking questions have you on the edge? Understanding blanked edge characteristics improves stamping. http://www.thefabricator.com/PressTechnology/PressTechnology_Article.cfm?ID=1165. Oct 10, 2005. Product News Network (PNN). New Minister Press Designed for Heavy Blanking Applications. http://news.thomasnet.com/fullstory/454769/1106. Aug 16, 2004. Oct 10, 2005.

Works cited continuedAluminum Extrusion Process

http://www.bsu.edu/web/jestanley/aluminumextrusion.htmEXTRUSION PROCESS

http://www.aec.org/cyberg/process.html#a3

Extrusion Process Description...

http://www.bonlalum.com/Login/SlsMfg/extrusion_process.jsp

Manufacturing Engineering and Technology

Serope Kalpakjian, Steven R. SchmidPrentice-Hall, Fifth Edition